Disregarding cat c*ckes for a moment!
I do agree that it is important to be happy with how you are. However, I don't think people are really quite so static as to consider their weight part of who the really are. A skinny dude could get into rock climbing and suddenly become slightly muscular. Or an overweight person could discover a love for soccer and lose a lot of it. I wouldn't say you'd have lost yourself in the process.
As for me, I am torn between being a computer programmer and loving the outdoors. So my school/career/hobby inspires a sedentary lifestyle, while I love to climb trees, walls, etc., and find adventures in the forests and mountains. As a result, I am dissatisfied with my current physique, because I know if I were slimmer I would find a lot more enjoyment in such wilderness tomfoolery. At the same time, I have people telling me that I am perfect as I am, but that is blatently false! Granted, I did approach almost-skinniness at the end of high school, and I think I look like an utter dork in pictures taken at those times, but I would gladly choose ability over appearance, so that is entirely irrelevant.
What is my point? Ah, that changing yourself is not always bad, and that it is a remarkably vain person who will not admit that they could use some change. You just have to find a middle ground between confidence and utility.
Ok, now for the cat c*ck discussions.